Conveyed object detector, conveyance device, device including movable head, conveyed object detecting method, and non-transitory recording medium storing program of same

ABSTRACT

A conveyed object detector includes first and second image obtaining units disposed at first and second positions different in a conveyance direction, to image a conveyed object to obtain first and second image data; respectively; a recognition unit to recognize an object adhering to the first and second image obtaining units based on imaging at the first and second positions to generate first and second stain data, respectively; a removal unit to remove the first and second stain data from the first and second image data, respectively; and a calculator to generate at least one of a position, a movement amount, and a moving speed of the conveyed object based on first and second corrected image data. Each of the first and second image obtaining units include a light source, an area sensor, and an optical element disposed between the area sensor and the conveyed object.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application Nos. 2016-115164, filedon Jun. 9, 2016, and 2017-111347, filed on Jun. 6, 2017, in the JapanPatent Office, the entire disclosure of which is hereby incorporated byreference herein.

BACKGROUND Technical Field

Embodiments of the present disclosure relate to a conveyed objectdetector, a conveyance device, an apparatus including a movable head toperform an operation on a conveyed object, a conveyed object detectingmethod, and a recording medium storing a program of the method.

Description of the Related Art

There are various types of operation using a movable head unit. Forexample, there are image forming methods that include discharging inkfrom a print head (so-called inkjet).

In such image forming methods, the position of the print head isadjusted to improve image quality.

SUMMARY

According to an aspect of this disclosure, a conveyed object detectorincludes a first image obtaining unit disposed at a first position toimage a conveyed object to obtain first image data; a second imageobtaining unit disposed at a second position different from the firstposition in a conveyance direction of the conveyed object. The secondimage obtaining unit is configured to image the conveyed object toobtain second image data. Each of the first image obtaining unit and thesecond image obtaining unit includes a light source to irradiate theconveyed object with light, an area sensor to receive reflected lightreflected from the conveyed object, and an optical element disposedbetween the area sensor and the conveyed object. The conveyed objectdetector further includes a recognition unit configured to recognize anobject adhering to the first image obtaining unit based on imaging atthe first position to generate first stain data, and recognize an objectadhering to the second image obtaining unit based imaging at the secondposition, to generate second stain data. The conveyed object detectorfurther includes a removal unit configured to remove the first staindata from the first image data, to generate first corrected image data,and remove the second stain data from the second image data to generatesecond corrected image data. The conveyed object detector furtherincludes a calculator configured to generate, as a calculation result,at least one of a position, a movement amount, and a moving speed of theconveyed object based on the first corrected image data and the secondcorrected image data.

In another aspect, a conveyance device includes a conveyance device toconvey the conveyed object and the conveyed object detector describedabove.

Another aspect provides an apparatus including a head unit to move in anorthogonal direction orthogonal to the conveyance direction and performan operation on the conveyed object. The device further includes theconveyance device described above and a head controller to control thehead unit, based on a detection result generated by the conveyed objectdetector.

Another aspect provides a conveyed object detector including imageobtaining means for imaging a conveyed object at a first position and asecond position to obtain first image data and second image data,respectively. The second position is different from the first positionin a conveyance direction of the conveyed object. The conveyed objectdetector further includes recognition means for recognizing an adheringobject included in imaging at the first position to generate first staindata, and an adhering object included in imaging at the second positionto generate second stain data. The conveyed object detector furtherincludes removal means for removing the first stain data from the firstimage data to generate first corrected image data and removing thesecond stain data from the second image data to generate secondcorrected image data. The conveyed object detector further includescalculating means for generating, as a calculation result, at least oneof a position, a movement amount, and a moving speed of the conveyedobject based on the first corrected image data and the second correctedimage data.

Another aspect provides a conveyed object detecting method that includesimaging, with a first area sensor and a second area sensor, a conveyedobject at a first position and a second position to obtain first imagedata and second image data, respectively. The second position isdifferent from the first position in a conveyance direction of theconveyed object. The method further includes recognizing an objectadhering to the first area sensor based on imaging at the firstposition, to generate first stain data, and recognizing an objectadhering to the second area sensor based imaging at the second position,to generate second stain data. The method further includes removing thefirst stain data from the first image data, to generate first correctedimage data, removing the second stain data from the second image data,to generate second corrected image data; and generating, as acalculation result, at least one of a position, a movement amount, and amoving speed of the conveyed object based on the first corrected imagedata and the second corrected image data.

Another aspect provides a computer-readable non-transitory recordingmedium storing a program for causing a computer to execute the methoddescribed above.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic view of an image forming apparatus as a liquiddischarge apparatus according to an embodiment;

FIG. 2 is a schematic view illustrating a general structure of the imageforming apparatus illustrated in FIG. 1;

FIG. 3A is a schematic view illustrating an external shape of a liquiddischarge head unit of the image forming apparatus illustrated in FIG.2;

FIG. 3B is a schematic view of a liquid discharge head of the liquiddischarge head unit illustrated in FIG. 3A;

FIG. 4 is a schematic block diagram illustrating a configuration of aconveyed object detector of the image forming apparatus illustrated inFIG. 2;

FIG. 5 is an external view of a sensor unit of conveyed object detectorillustrated in FIG. 4;

FIG. 6 is a schematic block diagram of a functional configuration of theconveyed object detector illustrated in FIG. 4;

FIGS. 7A and 7B are plan views of a meandering recording medium (acontinuous sheet;

FIG. 8 is a plan view of an image out of color registration on themeandering recording medium;

FIG. 9 is a schematic block diagram of a configuration of a controllerof the image forming apparatus illustrated in FIG. 2;

FIG. 10 is a block diagram of a configuration of a data management unitof the controller illustrated in FIG. 9;

FIG. 11 is a block diagram of a configuration of an image output of thecontroller illustrated in FIG. 9;

FIG. 12 is a flowchart of processing performed by the conveyed objectdetector illustrated in FIG. 6;

FIGS. 13A, 13B, and 13C are views of examples of perception of anadhering object according to an embodiment;

FIG. 14 is a diagram of example results of correlation operationaccording to an embodiment;

FIG. 15 is a side view of the image forming apparatus illustrated inFIG. 1;

FIGS. 16A and 16B are schematic diagrams illustrating operation of theimage forming apparatus illustrated in FIG. 15;

FIG. 17 is a plan view illustrating a location of the sensor unitaccording to an embodiment;

FIG. 18 is a plan view illustrating arrangement of the sensor unitsaccording to an embodiment;

FIG. 19 is a plan view of a web conveyed in an image forming apparatusaccording to Comparative example 1;

FIG. 20 is a schematic diagram illustrating operation of the imageforming apparatus according to Comparative example 1;

FIG. 21 is a schematic diagram illustrating operation of the imageforming apparatus according to Comparative example 2;

FIG. 22 illustrates an example location of a sensor unit in the imageforming apparatus illustrated in FIG. 21;

FIG. 23 is a schematic view of a sensor unit according to an embodiment;

FIG. 24 is a schematic block diagram of a functional configuration ofthe conveyed object detector according to an embodiment;

FIG. 25 is a schematic block diagram of a conveyed object detectoraccording to Variation 1;

FIG. 26 is a schematic view of an imaging unit of the conveyed objectdetector according to Variation 2;

FIGS. 27A and 27B are schematic views of a conveyed object detectoraccording to Variation 3;

FIG. 28 is a schematic view of a plurality of imaging lenses used forthe detecting the conveyed object, according to another variation; and

FIG. 29 is a schematic view of an image forming apparatus according toanother variation.

The accompanying drawings are intended to depict embodiments of thepresent invention and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected, and it is to be understood that eachspecific element includes all technical equivalents that operate in asimilar manner and achieve a similar result.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views thereof,and particularly to FIG. 1, an image forming apparatus according to anembodiment of the present invention is described. As used herein, thesingular forms “a”, “an”, and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise.

In the embodiment described below, a liquid discharge head unit is oneexample of a movable head, and a liquid discharge apparatus is oneexample of an apparatus including the movable head.

FIG. 1 is a schematic view of an image forming apparatus, serving as aliquid discharge apparatus, according to an embodiment. In FIG. 1, animage forming apparatus 110 discharges a recording liquid such asaqueous ink or oil-based ink. Additionally, the image forming apparatus110 is an example of a conveyance device to convey a conveyed objectsuch as a recording medium.

In this example, the conveyed object is a web 120. In the illustratedexample, the image forming apparatus 110 includes a roller 130 and thelike to convey the web 120, serving as a recording medium, anddischarges liquid onto the web 120 to form an image thereon. The web 120is a so-called continuous sheet. That is, the web 120 is, for example,paper in the form of roll that can be reeled. The image formingapparatus 110 is a so-called production printer. The description belowconcerns an example in which the roller 130 adjusts the tension of theweb 120 and conveys the web 120 in a conveyance direction 10.Hereinafter, unless otherwise specified, “upstream” and “downstream”mean those in the conveyance direction 10. A direction orthogonal to theconveyance direction 10 is referred to as an orthogonal direction 20. Inthe illustrated example, the image forming apparatus 110 is an inkjetprinter to discharge four color inks, namely, black (K), cyan (C),magenta (M), and yellow (Y) inks, to form an image on the web 120.

Note that the suffixes K, C, M, and K attached to each reference numeralindicate that components indicated thereby are used for forming black,cyan, magenta, and yellow, images, respectively, and hereinafter may beomitted when color discrimination is not necessary.

FIG. 2 is a schematic view of the image forming apparatus 110. Asillustrated in FIG. 2, the image forming apparatus 110 includes fourliquid discharge head units 210 (210K, 210C, 210M, and 210Y) todischarge the four inks, respectively.

Each liquid discharge head unit 210 discharges the ink onto the web 120conveyed in the conveyance direction 10. The image forming apparatus 110includes two pairs of nip rollers, a roller 230 (e.g., a drivingroller), and the like, to convey the web 120. One of the two pairs ofnip rollers is a first nip roller pair NR1 disposed upstream from theliquid discharge head units in the conveyance direction 10. The other isa second nip roller pair NR2 disposed downstream from the first niproller pair NR1 and the liquid discharge head units in the conveyancedirection 10. Each nip roller pair rotates while nipping the conveyedobject, such as the web 120, as illustrated in FIG. 2. The nip rollerpairs and the roller 230 as conveyors convey the conveyed object (e.g.,the web 120) in a predetermined direction.

The web 120 is a long sheet of recording media. Specifically, therecording medium is preferably longer than the distance between thefirst nip roller pair NR1 and the second nip roller pair NR2. Therecording medium is not limited to webs. For example, the recordingmedium may be a folded sheet (so-called fanfold paper or Z-fold paper).

In the structure illustrated in FIG. 2, the liquid discharge head units210 are arranged in the order of black, cyan, magenta, and yellow in theconveyance direction 10. Specifically, the liquid discharge head unit210K for black is disposed extreme upstream, and the liquid dischargehead unit 210C for cyan is disposed next to and downstream from theliquid discharge head unit 210K. Further, the liquid discharge head unit210M for magenta is disposed next to and downstream from the liquiddischarge head unit 210C for cyan, and the liquid discharge head unit210Y for yellow is disposed extreme downstream in the conveyancedirection 10.

Each liquid discharge head unit 210 discharges ink droplets so that theink droplets strike a predetermined position on the web 120, accordingto image data. The position at which the liquid discharge head unit 210discharges ink (hereinafter “ink discharge position”) is almostidentical to the position at which ink droplets discharged from theliquid discharge head (e.g., 210K-1, 210K-2, 210K-3, or 210K-4 in FIG.3A) strike the surface of the recording medium. In other words, the inkdischarge position can be directly below the liquid discharge head. Inthe present embodiment, black ink is discharged to the ink dischargeposition of the liquid discharge head unit 210K (hereinafter “black inkdischarge position PK”). Similarly, cyan ink is discharged to the inkdischarge position of the liquid discharge head unit 210C (hereinafter“cyan ink discharge position PC”). Magenta ink is discharged to the inkdischarge position of the liquid discharge head unit 210M (hereinafter“magenta ink discharge position PM”). Yellow ink is discharged to theink discharge position of the liquid discharge head unit 210Y(hereinafter “yellow ink discharge position PY”). Note that a controller520 operably connected to the liquid discharge head units 210 controlsthe respective timings at which the liquid discharge head units 210discharge ink.

In the description below, the ink discharge position serves as anoperation position of the liquid discharge head unit.

Each liquid discharge head unit 210 is provided with a plurality ofrollers. As illustrated in the drawings, for example, the image formingapparatus 110 includes the rollers respectively disposed upstream anddownstream from each liquid discharge head unit 210. In the illustratedexample, a first roller CR1, serving as a first support, is disposedupstream from each liquid discharge head unit 210 to convey the web 120to the ink discharge position. Similarly, a second roller CR2, servingas a second support, is disposed downstream from each liquid dischargehead unit 210 to convey the web 120 from the ink discharge position.Disposing the first roller CR1 and the second roller CR2 for each inkdischarge position can suppress fluttering of the recording mediumconveyed. For example, the first roller CR1 and the second rollerCR2used to convey the recording medium are driven rollers.Alternatively, the first roller CR1 and the second roller CR2 may bedriven by a motor or the like.

Note that, instead of the first and second roller CR1 and CR2 that arerotators such as driven rollers, first and second supports to supportthe conveyed object may be used. For example, each of the first andsecond supports can be a pipe or a shaft having a round cross section.Alternatively, each of the first and second supports can be a curvedplate having a curved face to contact the conveyed object. In thedescription below, the first and second supporters are rollers.

Specifically, a first roller CR1K, disposed upstream from the liquiddischarge head unit 210K, conveys the web 120 to the black ink dischargeposition PK so that black ink is applied to a specific portion of theweb 120. A second roller CR2K conveys the web 120 from the black inkdischarge position PK to the downstream side. Similarly, a first rollerCR1C and a second roller CR2C are disposed upstream and downstream fromthe liquid discharge head unit 210C for cyan, respectively. Similarly, afirst roller CR1M and a second roller CR2M are disposed upstream anddownstream from the liquid discharge head unit 210M, respectively.Similarly, a first roller CR1Y and a second roller CR2Y are disposedupstream and downstream from the liquid discharge head unit 210Y,respectively.

An example outer shape of the liquid discharge head unit 210 isdescribed below with reference to FIGS. 3A and 3B. FIG. 3A is aschematic plan view of one of the four liquid discharge head units 210K,210C, 210M, and 210Y of the image forming apparatus 110.

As illustrated in FIG. 3A, the liquid discharge head unit 210 accordingto the present embodiment is a line-type head unit. That is, the imageforming apparatus 110 includes the four liquid discharge head units210K, 210C, 210M, and 210Y arranged in the order of black, cyan,magenta, and yellow in the conveyance direction 10.

The liquid discharge head unit 210K includes four heads 210K-1, 210K-2,210K-3, and 210K-4 arranged in a staggered manner in the orthogonaldirection 20 orthogonal to the conveyance direction 10 in which the web120 is conveyed. With this arrangement, the image forming apparatus 110can form an image across the image formation area in the width directionorthogonal to the conveyance direction 10. The liquid discharge headunits 210C, 210M, and 210Y are similar in structure to the liquiddischarge head unit 210K, and the descriptions thereof are omitted toavoid redundancy.

Although the liquid discharge head unit 210 includes the four heads inthe description above, alternatively, the liquid discharge head unit 210may be constructed of a single head.

[Sensor]

The image forming apparatus 110 includes, for each liquid discharge headunit 210, a sensor unit SEN to detect the surface of the recordingmedium in the conveyance direction 10 or the orthogonal direction 20.Usable as the sensor unit SEN are a sensor employing laser, airpressure, photoelectric, or ultrasonic; and an optical sensor employinglight such as infrared. For example, the optical sensor is acharge-coupled device (CCD) camera or a complementary metal oxidesemiconductor (CMOS) camera. The sensor unit SEN serving as an imageobtaining unit is a sensor to detect a surface of the recording mediumduring image formation, thereby detecting at least one of the position,speed, the amount of movement of the recording medium.

As illustrated in FIG. 2, a setting unit 55F is coupled to the sensorunit SEN. The setting unit 55F sets an aperture relating to the sensor,exposure time, and the like based on computation result of the sensor orthe controller 520. The setting is described in further detail later.

FIG. 4 is a schematic block diagram illustrating a configuration of aconveyed object detector 500 according to an embodiment. For example,the conveyed object detector 500 includes an imaging unit 16, an imagingcontroller 14, an image memory 15, and a calculator 53F. The imagingunit 16, the imaging controller 14, the image memory 15 together formsan image obtaining unit 52 (e.g., 52A or 52B in FIG. 6) to image theconveyed object and generate image data thereof.

The imaging unit 16 is implemented by the following structure.

FIG. 5 is an external view of the sensor unit SEN functioning as theimaging unit 16. The sensor unit SEN illustrated in FIG. 5 is configuredto capture a speckle pattern, which appears on a conveyed object (i.e.,a target in FIG. 5) such as a recording media when the conveyed objectis irradiated with light. Specifically, the sensor unit SEN includes alight source 51 such as semiconductor laser light source (e.g., a laserdiode or LD) and an optical element such as a collimate optical system510. To obtain an image having a speckle pattern, the sensor unit SENfurther includes a complementary metal oxide semiconductor (CMOS) imagesensor 511 and a telecentric optical system 512 to condense light toimage the speckle pattern on the CMOS image sensor 511. The telecentricoptical system 512 is disposed between the image sensor 511 serving asan area sensor and the conveyed object (i.e., a target in FIG. 5).

In the structure illustrated in FIG. 5, the CMOS image sensor 511captures the image having the speckle pattern at multiple times, at atime TM1 (a first time point) and a time TM2 (a second time point).Based on the imaging at the time TM1 and the imaging at the time TM2, acalculator 53F of the controller 520 performs cross-correlationoperation and the like. The calculator 53F may be implemented by afield-programmable gate array (FPGA) circuit 508. Alternatively, thecalculator 53F is implemented by the controller 520 of the image formingapparatus 110. Based on a displacement of a correlation peak positioncalculated by the correlation operation or the like, the conveyed objectdetector 500 outputs the amount of movement of the conveyed object(e.g., the recording medium) from the time TM1 to the time TM2. In theillustrated example, the sensor unit SEN has a width W of 15 mm, a depthD of 60 mm, and a height H of 32 mm (15×60×32). The correlationoperation is described in detail later.

The CMOS image sensor 511 is an example hardware structure to implementthe imaging unit 16 constructing an image obtaining unit 52 (52A and 52Bin FIG. 6). The FPGA circuit 508 is an example hardware structure of theimaging controller 14 and image memory 15.

Referring back to FIG. 4, the imaging controller 14 controls the imagingunit 16 and the like. Specifically, for example, the imaging controller14 outputs trigger signals to the imaging unit 16 to control the timingof shooting (shutter timing) of the CMOS image sensor 511. The imagingcontroller 14 causes the imaging unit 16 to generate the two-dimensionalimages and acquires the two-dimensional images therefrom. Then, theimaging controller 14 transmits the two-dimensional images generated bythe imaging unit 16 to the image memory 15.

The image memory 15 is a so-called memory. The image memory 15preferably has a capability to divide the two-dimensional imagestransmitted from the imaging controller 14 or the like and store thedivided images in different memory ranges.

For example, the calculator 53F is a microcomputer. The calculator 53Fperforms operations using the image data stored in the image memory 15and the like, to implement a variety of processing.

The imaging controller 14 and the calculator 53F are, for example,central processing units (CPUs) or electronic circuits. Note that theimaging controller 14, the image memory 15, and the calculator 53F arenot necessarily discrete devices. For example, the imaging controller 14and the calculator 53F can be implemented by a single CPU.

The conveyed object detector 500 is described in further detail below,using an example including two optical systems identical to the opticalsystem illustrated in FIG. 5. The number of the optical systems is notlimited to two but can be one or greater than two. Each optical systemmay have a diaphragm, such as, a motorized iris diaphragm. The diaphragmis controlled by an actuator or the like to adjust the amount of lightreceived. Alternatively, shutter speed or the like may be controlled toadjust exposure time. For example, the imaging controller 14 performscontrol processing, and the setting unit 55F sets the aperture and thelike.

FIG. 6 is a schematic block diagram of a functional configuration of theconveyed object detector 500 according to an embodiment. As describedabove, the image obtaining unit 52 (implemented by the sensor unit SEN)is provided for each of the liquid discharge head units 210. In thepresent embodiment, the amount of movement of the conveyed object andthe like are calculated based on two of the sensor units SEN.Descriptions below are based on a combination of black and cyan. In thisexample, as illustrated in FIG. 6, the image obtaining unit 52A for theliquid discharge head unit 210K outputs a detection result concerningthe position A, and the image obtaining unit 52B for the liquiddischarge head unit 210C outputs a detection result concerning theposition B. The image obtaining unit 52A for the liquid discharge headunit 210K includes, for example, an imaging unit 16A, an imagingcontroller 14A, and an image memory 15A. In this example, the imageobtaining unit 52B for the liquid discharge head unit 210C is similar inconfiguration to the image obtaining unit 52A. The image obtaining unit52B includes an imaging unit 16B, an imaging controller 14B, and animage memory 15B. The image obtaining unit 52A is described below.

As illustrated in FIG. 6, the imaging unit 16A captures an image of theweb 120 conveyed in the conveyance direction 10. The imaging unit 16A isimplemented by the CMOS image sensor 511 (illustrated in FIG. 5).

The imaging controller 14A includes an image acquisition unit 142A. Theimaging controller 14A is implemented by, for example, a CPU, electriccircuitry, and the like.

The image acquisition unit 142A captures the image generated by theimaging unit 16A.

The imaging controller 14A may include a shutter controller 141A and thelike. The shutter controller 141A controls the timing of imaging by theimaging unit 16A. In the example described below, the imaging controller14A includes the shutter controller 141A.

The image memory 15A (implemented by a so-called memory) stores theimage data captured by the imaging controller 14A.

The calculator 53F calculates, based on data of the image data recordedin the image memories 15A and 15B, the position of a pattern on the web120, the speed at which the web 120 moves (hereinafter “moving speed”),and the amount of movement of the web 120. Additionally, the calculator53F outputs, to the shutter controller 141A, data on time difference Δtindicating the timing of shooting (shutter timing). In other words, thecalculator 53F instructs the shutter controller 141A of shutter timingsof imaging at the position A and imaging at the position B with the timedifference Δt. The calculator 53F may also control the motor and thelike to convey the web 120 at the calculated moving speed. Thecalculator 53F can be implemented by a CPU or an electronic circuit.

The web 120 has diffusiveness on a surface thereof or in an interiorthereof. Accordingly, when the web 120 is irradiated with laser light,the reflected light is diffused. The diffuse reflection represents apattern on the web 120. The pattern is made of spots called “speckle”(i.e., a speckle pattern). Accordingly, when the web 120 is imaged, animage of the speckle pattern is obtained. From the image, the positionof the speckle image can be known, and the location of a specificportion of the web 120 can be detected. Such a speckle is generated asthe laser light emitted to the web 120 interferes with a rugged shape onthe surface of or inside the web 120.

As the web 120 is conveyed, the speckle pattern on the web 120 isconveyed as well. When an identical speckle pattern is detected atdifferent time points, the amount of movement of the speckle pattern isobtained. In other words, the calculator 53F obtains the amount ofmovement of the speckle pattern based on the detection of an identicalspeckle pattern, thereby obtaining the amount of movement of the web120. Further, the calculator 53F converts the calculated amount ofmovement into an amount of movement per unit time, thereby obtain themoving speed of the web 120.

The time difference Δt can be expressed by Formula 1, where V representsthe moving speed (mm/s), and L represents a relative distance, which isthe distance (mm) between a first imaging lens 12A and a second imaginglens 12B (illustrated in FIG. 23) in the conveyance direction 10.Δt=L/V  Formula 1

The relative distance L (mm) in Formula 1 is obtained preliminarily.When the time difference Δt is determined, the calculator 53F obtainsthe moving speed V according to Formula 1. Thus, based on the specklepattern, the image obtaining unit 52A can obtain the position of the web120 in the conveyance direction 10, the amount of movement, the movingspeed, or the combination thereof. The image obtaining unit 52A mayoutput a combination of two or more of the position of the web 120 inthe conveyance direction 10, the amount of movement, and the movingspeed.

As illustrated in FIG. 6, the imaging unit 16A and the imaging unit 16Bis spaced apart in the conveyance direction 10. Via the imaging unit 16Aand the imaging unit 16B, images of the web 120 are taken at therespective positions. Then, based on the speckle pattern, the calculator53F can generate a calculation result indicating the position of the web120 in the conveyance direction 10 or the orthogonal direction 20, witha high accuracy.

The image obtaining unit 52A may generate a detection result indicatingrelative positions, for example, representing the difference between aposition detected by one sensor unit SEN (i.e., the imaging unit 16A)and a position detected by another sensor unit SEN (i.e., the imagingunit 16B). Alternatively, one of the sensors may take a plurality ofimages, and the relative positions represent a difference between theposition on one image and the position on another image taken by thesame sensor unit SEN. That is, the relative positions can be, forexample, the difference between the position detected in a previousframe and the position detected in a subsequent frame. Thus, therelative positions indicate a displacement amount from a positiondetected in the previous frame or a position detected by another sensorunit SEN.

Alternatively, the sensor unit SEN may detect a position in theconveyance direction 10. The sensor unit SEN may be shared for detectinga position in the conveyance direction 10 and detecting a position inthe orthogonal direction 20, which reduces the cost of detectingpositions in both directions. Additionally, the space for the detectioncan be small since the number of sensors is reduced.

Further, the calculator 53F performs cross-correlation operation offirst image data D1(n) generated by the imaging unit 16A and secondimage data D2(n) generated by the imaging unit 16B. Hereinafter an imagegenerated by the cross-correlation operation is referred to as“correlated image”. For example, based on the correlated image, thecalculator 53F calculates the displacement amount ΔD(n), which is theamount of displacement from the position detected with the previousframe or by another sensor.

For example, the cross-correlation operation is expressed by Formula 2below.D1*D2*=−1[F[D1]·F[D2]*]  Formula 2

where D1 represents the first image data being the image taken by theposition A, and D2 represents the second image data being the imagetaken by the position B. In Formula 2, “F[ ]” represents Fouriertransform, “F−1[ ]” represents inverse Fourier transform, “*” representscomplex conjugate, and “*” represents cross-correlation operation.

As represented in Formula 2, image data representing the correlationimage is obtained through cross-correlation operation “D1*D2” performedon the first image data D1 and the second image data D2. Note that, whenthe first image data D1 and the second image data D2 are two-dimensionalimage data, the image data representing the correlation image istwo-dimensional image data. When the first image data. D1 and the secondimage data D2 are one-dimensional image data, the image datarepresenting the correlation image is one-dimensional image data.

Regarding the correlation image, when a broad luminance distributioncauses an inconvenience, phase only correlation can be used. Forexample, phase only correlation is expressed by Formula 3 below.D1*D2*=F−1[P[F[D1]]·P[F[D2]*]]  Formula 3

In Formula 3, “P[ ]” represent taking only phase out of complexamplitude. Note that the amplitude is considered to be “1”.

Thus, the calculator 53F can obtain the displacement amount ΔD(n) basedon the correlation image even when the luminance distribution isrelatively broad.

The correlation image represents the correlation between the first imagedata D1 and the second image data D2. Specifically, as the match ratebetween the first image data D1 and the second image data D2 increases,a luminance causing a sharp peak (so-called correlation peak) is outputat a position close to a center of the correlation image. When the firstimage data D1 matches the second image data D2, the center of thecorrelation image and the peak position overlap.

Based on the displacement in the orthogonal direction 20 (widthdirection) and the like thus calculated, the head controller 54Fcontrols the actuator to move the liquid discharge head unit 210C in thewidth direction and discharge liquid. Additionally, based on thedisplacement in the conveyance direction 10, the liquid discharge headunit 210C discharges the liquid. Note that the timing of ink dischargeis controlled with a second signal SIG2 for the liquid discharge headunit 210C (a first signal SIG1 is for the liquid discharge head unit210K). As illustrated, based on the calculation by the calculator 53F,the head controller 54F outputs the signal to control the position ofthe liquid discharge head unit 210 in the width position and the timingsof the liquid discharge head unit 210. The head controller 54F isimplemented by, for example, the controller 520.

The calculator 53F outputs the moving speed V calculated based on thedetection result, to a setting unit 55F. The setting unit 55F calculatesthe aperture, the exposure time, or both, based on the moving speed Vtransmitted from the calculator 53F. To the setting unit 55F, the movingspeed V may be input, according to an operation setting (or operatingmode) such as resolution of images output from the image formingapparatus 110. The setting unit 55F can be implemented by a microcomputer or the like.

The setting unit 55F may perform setting according to the moving speed VSpecifically, when the moving speed V is relatively high, the settingunit 55F sets the exposure time and the aperture to reduced values. Bycontrast, when the moving speed V is relatively low, the setting unit55F sets the exposure time and the aperture to increased values. Thus,the aperture may be set according to the moving speed V.

Then, a diaphragm controller implemented by the imaging controller 14(illustrated in FIG. 4), an actuator, and the like, adjusts thediaphragm to attain the aperture set by the setting unit 55F.

Similarly, the shutter controllers 141A and 141B may control the shutterspeed to attain the exposure time set by the setting unit 55F.

Thus, the imaging units 16A and 16B can perform imaging based on theexposure time and the aperture associated with the moving speed V.Alternatively, the controller 520 may perform the calculation and thesetting.

Specifically, the aperture is calculated to achieve a received lightamount inversely proportional to the exposure time determined by themoving speed V. For example, the aperture is calculated according toFormula 4 below.I=Io×(NA×Mo)²DF=±k×WL/{2×(NA)^(2})  Formula 4

where “I” represents the brightness of an image, “Io” represents thebrightness of the surface of a sample. Further, in Formula 4, “NA”represents the number of apertures (openings), “Mo” represents themagnification of an objective, “DF” represents depth of focus, and “WL”represents wavelength. That is, the number of apertures is set at thediaphragm. In the case of Formula 4, the received light amount isproportional to the square of the number of apertures. Accordingly, whenthe exposure time is set to “half”, the number of apertures is “√2”.

The empirically obtained exposure time and the aperture associated withthe moving speed V can be stored, in a data form such as a lookup table,in the image memory 15. The setting unit 55F retrieves an exposure timevalue and an aperture value associated with the moving speed V from thelookup table or the like and sets the exposure time and the aperture tothe retrieved values.

Referring back to FIG. 2, in the description below, the sensor unitsSENK, SENC, SENM, and SENY respectively provided for the liquiddischarge head units 210K, 210C, 210M, and 210Y may be collectivelyreferred to as “sensor units SEN”.

Further, the term “location of the sensor unit SEN” means the positionwhere the detection is performed. Accordingly, it is not necessary thatall components relating to the detection are disposed at the “locationof the sensor unit SEN”. Some of the components may be connected to thesensor unit SEN via a cable and disposed away therefrom. In FIG. 2,references “SENK, SENC, SENM, and SENY” represent respective examplelocations of the liquid discharge head units 210K, 210C, 210M, and210Y″.

Preferably, the location of the sensor unit SEN is close to the inkdischarge position. That is, the distance between the ink dischargeposition and the sensor unit SEN is preferably short. When the distancebetween the ink discharge position and the sensor unit SEN is short,detection error can be suppressed. Accordingly, in the image formingapparatus 110, the sensor unit SEN can detect the position of therecording medium in the conveyance direction 10 or the orthogonaldirection 20, with a high accuracy.

Specifically, the sensor unit SEN is disposed between the first rollerCR1 and the second roller CR2. In the illustrative embodiment, thesensor unit SENK for black is preferably disposed in an inter-rollerrange INTK1 between the first and second rollers CR1K and CR2K.Similarly, the sensor unit SENC for cyan is preferably disposed in aninter-roller range INTC1 between the first and second rollers CR1C andCR2C. The sensor unit SENM for magenta is preferably disposed in aninter-roller range 1NTM1 between the first and second rollers CR1M andCR2M. The sensor unit SENY for yellow is preferably disposed in aninter-roller range INTY1 between the first and second rollers CRIY andCR2Y. The inter-roller ranges INTY1, INTC1, INTM1, and INTY1 arecollectively referred to as “inter-roller ranges INT1”. The sensor unitSEN disposed between the first and second rollers CR1 and CR2 can detectthe recording medium at a position close to the ink discharge position.Further, since the moving speed V is relatively stable in a portionbetween the rollers, the image forming apparatus 110 can detect theposition of the recording medium in the conveyance direction 10 or theorthogonal direction 20, with a high accuracy.

More preferably, in each inter-roller ranges INT1, the sensor unit SENis disposed between the ink discharge position and the first roller CR1(closer to the first roller CR1 than the ink discharge position). Inother words, the sensor unit SEN is preferably disposed upstream fromeach ink discharge position in the conveyance direction 10.

Specifically, the sensor unit SENK for black is, more preferably,disposed in a range extending from the black ink discharge position PKupstream to the first roller CR1K for black in the conveyance direction10 (hereinafter “upstream range INTK2”). Similarly, the sensor unit SENCfor cyan is, more preferably, disposed in a range extending from thecyan ink discharge position PC upstream to the first roller CR1C forcyan (hereinafter “upstream range INTC2”). The sensor unit SENM formagenta is, more preferably, disposed in a range extending from themagenta ink discharge position PM upstream to the first roller CR1M formagenta (hereinafter “upstream range INTM2”). The sensor unit SENY foryellow is, more preferably, disposed in a range extending from theyellow ink discharge position PY upstream to the first roller CR1Y foryellow (hereinafter “upstream range INTY2”).

When the sensor units SEN are respectively disposed in the upstreamranges INTK2, INTC2, INTM2, and INTY2, the image forming apparatus 110can detect the recording medium (conveyed object) with a high accuracy.The sensor unit SEN thus disposed is upstream from the position at whichink droplets strike the recording medium (also “droplet strikeposition”) in the conveyance direction 10. Therefore, in the imageforming apparatus 110, the sensor unit SEN can accurately detect theposition of the recording medium in the conveyance direction 10, theorthogonal direction 20, or both, at a position upstream from thedroplet strike position. Accordingly, the controller 520 (or thecalculator 53F) can calculate respective ink discharge timings (i.e.,operation timing) of the liquid discharge head units 210, the amount bywhich the head unit is to move (i.e., head moving amount), or both. Inother words, in a period from when the position of a given portion ofthe web 120 is detected on the upstream side of the droplet strikeposition to when the detected portion of the web 120 reaches the dropletstrike position, the operation timing is calculated or the head unit ismoved. Therefore, the image forming apparatus 110 can change the dropletstrike position with high accuracy.

Note that, assuming that the sensor unit SEN is disposed directly belowthe liquid discharge head unit 210, in some cases, a delay of controlaction renders an image out of color registration. Accordingly,disposing the sensor unit SEN upstream from the droplet strike positioncan suppress misalignment in color superimposition and improve imagequality. There are cases where layout constraints hinder disposing thesensor unit SEN adjacent to the droplet strike position. Accordingly,the sensor unit SEN is preferably disposed closer to the first rollerCR1 than the ink discharge position.

As in the example described below, the sensor unit SEN can be disposeddirectly below each liquid discharge head unit 210. The sensor unit SENdisposed directly below the head unit can accurately detect the amountof movement of the recording medium directly below the head unit.Therefore, in a configuration in which the speed of control action isrelatively fast, the sensor unit SEN is preferably disposed closer tothe position directly below each liquid discharge head unit 210.However, the position of the sensor unit SEN is not limited to aposition directly below the liquid discharge head unit 210, and similarcalculation is feasible when the sensor unit SEN is disposed otherwise.

Alternatively, in a configuration where error is tolerable, the sensorunit SEN can be disposed directly below the liquid discharge head unit210, or downstream from the position directly below the liquid dischargehead unit 210 in the inter-roller range INT1.

The image forming apparatus 110 may further includes a measuringinstrument such as an encoder, as described bellow. For example, theencoder is attached to a rotation shaft of the roller 230 (i.e., thedriving roller). Then, the encoder can measure the amount of movement ofthe web 120 in the conveyance direction 10, based on the amount ofrotation of the roller 230. When the measurement results are used incombination with the detection results generated by the sensor unit SEN,the liquid discharge head unit 210 can discharge ink to the web 120accurately.

Descriptions are given below of fluctuations of the recording medium inthe orthogonal direction 20, with reference to FIGS. 7A and 7B. FIGS. 7Aand 7B are plan view of the web 120 being conveyed. In FIG. 7A, whilethe web 120 is conveyed in the conveyance direction 10 by the rollers(such as the rollers 230, CR1, and CR2 in FIG. 2), the position of theweb 120 may fluctuate in the orthogonal direction 20 as illustrated inFIG. 7B. That is, the web 120 may meander as illustrated in FIG. 7B.

The fluctuation of the position of the web 120 in the orthogonaldirection 20 (hereinafter “orthogonal position of the web 120”), thatis, the meandering of the web 120, is caused by eccentricity of aconveyance roller (the driving roller in particular), misalignment, ortearing of the web 120 by a blade. When the web 120 is relatively narrowin the orthogonal direction 20, for example, thermal expansion of theroller affect fluctuation of the web 120 in the orthogonal position.

Descriptions are given below of a cause to render images out of colorregistration, with reference to FIG. 8. Due to fluctuations (meanderingillustrated in FIG. 7B) of the web 120 in the orthogonal position,images become out of color registration as illustrated in FIG. 8.

Specifically, to form a multicolor image on a recording medium using aplurality of colors, the image forming apparatus 110 superimposes aplurality of different color inks discharged from the liquid dischargehead units 210, through so-called color plane, on the web 120.

As illustrated in FIG. 7B, the web 120 can fluctuate in position and,for example, meanders with reference to lines 320 illustrated in FIG. 8.Assuming that the liquid discharge head units 210 discharge respectiveinks to an identical portion (i.e., an intended droplet strike position)on the web 120 in this state, a portion 330 out of color registration iscreated since the intended droplet strike position fluctuate in theorthogonal direction 20 while the web 120 meanders between the liquiddischarge head units 210. The portion 330 out of color registration iscreased as the position of a line or the like, drawn by the respectiveinks discharged from the liquid discharge head units 210, shakes in theorthogonal direction 20. The portion 330 out of color registrationdegrades the quality of the image on the web 120.

FIG. 9 is a schematic block diagram of an image forming system includinga server 71 serving as a higher-order device (e.g., an informationprocessing apparatus), and the image forming apparatus 110. In theillustrated example, the controller 520 includes a control board 520-1and an engine board 520-2. The control board 520-1 instructs the engineboard 520-2 on image formation according to image data and control datainput from the server 71.

The higher-order device is not limited to the server 71 but can be aclient computer (personal computer or PC) or a host device. Although thecontroller 520 includes the control board 520-1 and the engine board520-2 in FIG. 9, the number of boards is not limited thereto.

The control board 520-1 governs operation of the engine board 520-2. Thecontrol board 520-1 transmits and receives the control data to and fromthe server 71 via a control line 70LC. The control board 520-1 furthertransmits and receives the control data to and from the engine board520-2 via a control line 72LC. Through such data transmission andreception, the control data indicating printing conditions and the likeare input to the control board 520-1. The control board 520-1 stores theprinting conditions, for example, in a resistor. The control board 520-1then controls the engine board 520-2 according to the control data toform an image based on print job data, that is, the control data.

The control board 520-1 includes a CPU 72Cp, a print control unit 72Cc,and a memory 72Cm. The CPU 72Cp and the print control unit 72Cc (e.g.,an electronic circuit) are connected to each other via a bus 72Cb tocommunicate with each other. The bus 72Cb is connected to the controlline 70LC via a communication interface or the like.

The CPU 72Cp controls the entire image forming apparatus 110 based on acontrol program and the like. That is, the CPU 72Cp is a processor aswell as a controller.

The print control unit 72Cc transmits and receives data indicating acommand or status to and from the engine board 520-2, based on thecontrol date transmitted from the server 71. Thus, the print controlunit 72Cc controls the engine board 520-2.

To the engine board 520-2, a plurality of data lines, namely, data lines70LD-C, 70LDM, 70LD-Y, and 70LD-K are connected. The engine board 520-2receives the image data from the server 71 via the plurality of datalines. Then, the engine board 520-2 governs image formation ofrespective colors, controlled by the control board 520-1.

The engine board 520-2 includes a plurality of data management units72EC, 72EM, 72EY, and 72EK (also collectively “data management units72E”), an image output 72Ei, and a conveyance control unit 72Ec, each ofwhich can be implemented by an electronic circuit.

FIG. 10 is a block diagram of a configuration of the data managementunit 72E. The plurality of data management units 72E can have anidentical configuration. The data management unit 72EC is describedbelow as a representative. Redundant descriptions are omitted.

The data management unit 72EC includes a logic circuit 72ECl and amemory 72ECm. As illustrated in FIG. 10, the logic circuit 72ECl isconnected via a data line 70LD-C to the server 71. The logic circuit72ECl is connected via the control line 72LC to the print control unit72Cc. That the logic circuit 72ECl is implemented by, for example, anapplication specific integrated circuit (ASIC) or a programmable logicdevice (PLD).

According to a control signal input from the control board 520-1(illustrated in FIG. 9), the logic circuit 72ECl stores, in the memory72ECm, the image data input from the server 71.

According to a control signal input from the control board 520-1, thelogic circuit 72ECl retrieves, from the memory 72ECm, cyan image dataIc. The logic circuit 72ECl then transmits the cyan image data Ic to theimage output 72Ei.

The memory 72ECm preferably has a capacity for storing image dataextending about three pages. With the capacity for storing image dataextending about three pages, the memory 72ECm can store the image datainput from the server 71, data image being used current image formation,and image data for subsequent image formation.

FIG. 11 is a block diagram of a configuration of the image output 72Ei.As illustrated in FIG. 11, the image output 72Ei includes an outputcontrol unit 72Eic to output respective color image data to the liquiddischarge head units 210K, 210C, 210M, and 210Y That is, the outputcontrol unit 72Eic controls the liquid discharge head units 210 based onthe image data input thereto.

The output control unit 72Eic controls the plurality of liquid dischargehead units 210 either simultaneously or individually. That is, theoutput control unit 72Eic receives timing commands and changes thetimings at which the liquid discharge head units 210 dischargerespective color inks. The output control unit 72Eic may control one ormore of the liquid discharge head units 210 based on the control signalinput from the control board 520-1 (illustrated in FIG. 9).Alternatively, the output control unit 72Eic may control one or more ofthe liquid discharge head units 210 based on user instructions.

In the example illustrated in FIG. 9, the image forming apparatus 110has different routes for inputting the image data from the server 71 andfor transmission and reception of control data, with the server 71 andthe image forming apparatus 110.

The image forming apparatus 110 may form single-color images using, forexample, black ink. In the case of single-color image formation usingblack ink, to accelerate image formation speed, the image formingapparatus 110 can include one data management unit 72E and four blackliquid discharge head units 210. In such as configuration, the pluralityof black liquid discharge head units 210 discharge black ink.Accordingly, the image formation speed is faster than that in theconfiguration using one black liquid discharge head unit 210.

The conveyance control unit 72Ec (in FIG. 9) controls a conveyancedevice 200 (illustrated in FIG. 2) to convey the web 120. The conveyancedevice 200 includes a motor coupled to the rollers (e.g., the roller 230and the first and second nip roller pairs NR1 and NR2) to convey the web120, a mechanism therefor, and a driver for conveying the web 120.

FIG. 12 is a flowchart of an example of operation performed by theconveyed object detector 500. The conveyed object detector 500 performsthe processing illustrated in FIG. 12 for each predetermined period. Theprocessing described below is performed either during image formation orduring an interval between image formation.

In the illustrated example, steps S11 and S13A are performed in parallelto steps S12 and S13B. However, the order of steps is not limitedthereto. Alternatively, steps S11 and S13A may be performed after orbefore steps S12 and S13B one after another.

At S11, the image obtaining unit 52A obtains the first image data D1,which is data of the imaging at the position A illustrated in FIG. 6.The first image data D1 is stored in the image memory 15A.

At S12, the image obtaining unit 52B obtains the second image data D2,which is data of the imaging at the position B illustrated in FIG. 6.The second image data D1 is stored in the image memory 15B.

Description are given below of recognition of an object (stains or dust,hereinafter referred to as “adhering object BD”) adhering to the sensorunit SEN, performed before image formation, or interval time(corresponding to non-image area on the web 120) during image formation.In one embodiment, the recognition is performed for each of theplurality of image obtaining units 52. Alternatively, the recognition isperformed in the two image obtaining units 52 used to obtain the firstand second image data D1 and D2. For example, the adhering object BD isrecognized as illustrated in FIGS. 13A through 13C, and stain data ispreliminarily stored in a stain data memory 58F.

FIGS. 13A, 13B, and 13C are illustrations of examples of recognition ofan adhering object BD. In FIGS. 13A to 13C, the adhering object is astain such as ink. FIGS. 13B to 13C are generated by superimposing imagedata of a plurality of images. Specifically, FIG. 13A is an example inwhich the number (N) of image is one (N=1). FIG. 13B is an example inwhich 10 images are superimposed (N=10). FIG. 13C is an example in which20 images are superimposed (N=20).

As illustrated in FIGS. 13A to 13C, the area of the image representingthe adhering object BD does not change (i.e., a changeless area) evenwhen the subject of imaging is changed. Accordingly, as the number ofsuperimposed images increases, the adhering object BD becomes clearer,as illustrated in FIG. 13C. Thus, the recognition unit 56F recognizesthe adhering object BD based on a plurality of image data. That is, therecognition unit 56F recognizes the changeless area on the imagegenerated by superimposing a plurality of images. The image formingapparatus 110 stores the data of adhering object BD (i.e., stain data)in the stain data memory 58F.

The number of superimposed images for recognizing the adhering object BDis determined by the processing time or the like.

For example, recognizing that the changeless area occupies apredetermined area or greater of the image, the recognition unit 56Fdetermined that the changeless area represents the adhering object BD.

To alleviate the degradation of detection accuracy caused by noise, forexample, the image forming apparatus 110 may compare a previous image ofthe adhering object BD with a current image of the adhering object BD.When the difference as a result of the comparison changes in a shortperiod, by an amount greater or smaller than a predetermined value, therecognition unit 56F again performs recognizing processing. Thus,degradation of detection accuracy caused by noise can be suppressed.

Further, when the recognition unit 56F recognizes that the amount ordegree of stain is equal to or greater than a threshold, an alert may beissued or a message may be displayed. When the range of the imageconsidered to represent the adhering object DB exceeds a predeterminedsize, the controller 520 determines that cleaning is necessary andoutputs an alert or message. When the adhering object BD is recognizedin the entire image or the entire image is considered to be filled withthe adhering object BD, the controller 520 may detect malfunction of theconveyed object detector 500 or malfunction of a component (e.g., aharness) relating to the conveyed object detector 500.

At S13A, a removal unit 57F (illustrated in FIG. 6) removes, from thefirst image data D1 stored as described above, the stain data (i.e.,first stain data) representing the adhering object BD adhering to theimage obtaining unit 52A or the optical system thereof.

In the first image data D1, the removal unit 57F rewrites the data ofthe range representing the adhering object BD to “0”, based on the firstimage data D1 stored in the image memory 15A. To rewrite the data to“0”, the removal unit 57F may perform, for example, multiplication.Thus, the removal unit 57F removes the first stain data from the firstimage data D1 to generate first corrected image data.

At S13B, the removal unit 57F removes, from the second image data D2,the stain data (second stain data) representing an adhering object BDadhering to the second image obtaining unit 52B. In a manner similar tothat performed at S13A, the removal unit 57F can rewrite the datarepresenting the adhering object BD to “0” to remove the second staindata from the second image data D2 to generate second corrected imagedata.

Note that, differently from the processing illustrated in FIG. 12, inanother embodiment, the removal unit 57F removes both of the first staindata and the second stain data from each of the first image data D1 andthe second image data D2. In this case, although the number of effectivepixel decreases, the noise can be suppressed better, improving thesignal-to-noise ratio.

At S14, the calculator 53F performs a correlation operation,specifically, a correlation operation on the first corrected image dataprocessed at S13A and the second corrected image data processed at S13B.For example, the correlation operation is expressed by Formula 2described above. The parameters of Formula 2 are described above.D1*D2*=F−1[F[D1]·F[D2]*]  Formula 2

When the correlation operation is performed according to Formula 2,image data representing the correlation image is obtained. As describedabove, when the first image data D1 and the second image data D2 aretwo-dimensional image data, the result of operation image istwo-dimensional image data. When the first image data D1 and the secondimage data D2 are one-dimensional image data, the result of operation isone-dimensional image data. From the result of operation, thedisplacement between the first image data D1 and the second image data.D2 and the like can be calculated.

FIG. 14 is a diagram of example results of correlation operationperformed by the calculator 53F, according to Formula 2. FIG. 14illustrates a profile of strength of correlation function. In FIG. 14, Xaxis and Y axis represent serial number of pixel. In the illustratedoperation results, on the background noise depending on ink mist andlighting amount profile, a peak corresponding to the amount of travel ofthe web 120 between the frames. Depending on the shape of profile of thebackground noise, there may be an error in the peak position detected.By contrast, when the adhering object BD is removed as in steps S13A andS13B in FIG. 12, the calculator 53F can reduce the noise caused by inkmist and background noise from the result of operation. That is, thecalculator 53F can improve signal-to-noise ratio (SNR). As such noise isreduced, effects of uneven lighting by the light source are suppressed.

Although the description above concerns a case where fluctuations arepresent in Y direction, the correlation peak occurs at a positiondisplaced in the X direction when there are fluctuations in the Xdirection.

With the above-described correlation operation, the calculator 53F cancalculate the displacement and the like even during image formation.

At S15 (illustrated in FIG. 12), the calculator 53F detects thecorrelation peak in the result of operation illustrated in FIG. 14. Whenthe noise of ink mist and background noise are reduced in the result ofoperation, the calculator 53F can accurately detect the displacement ofthe correlation peak from the center.

At S16 in FIG. 12, the calculator 53F performs position calculation,specifically, calculates the amount of movement of the web 120 (conveyedobject) in the orthogonal direction, based on the correlation peakdetected at S15, as illustrated in FIG. 14. That is, the calculator 53Fcan calculate so-called meandering amount of the web 120 from theposition of the correlation peak.

With reference to FIGS. 15, 16A and 16B, descriptions are given below ofprocessing performed by the liquid discharge apparatus according to oneembodiment. In FIGS. 15, 16A, and 16B, the sensor units SEN are disposeddirectly below the respective liquid discharge head units 210. However,the locations of the sensor units SEN are not limited thereto as long asclose to the respective ink discharge positions. That is, the sensorunits SEN are disposed to accurately detect the position of the web 120at the respective ink discharge positions. For example, each sensor unitSEN is disposed between the first roller CR1 and the second roller CR2.

In the example illustrated in FIG. 15, inks are discharged in the orderof black, cyan, magenta, and yellow. FIG. 16B is a plan view of theimage forming apparatus 110 illustrated in FIG. 15. Descriptions aregiven below of a case where the roller 230 (i.e., the driving roller)has eccentricity, for example eccentricity EC illustrated in FIG. 16A.The eccentricity EC of the roller 230, which is the driving roller,causes oscillation OS or sway of the roller 230 as the web 120 isconveyed. With the oscillation OS, a position POS of the web 120 in theorthogonal direction 20 fluctuates. That is, the oscillation OS causes“meandering”. In the illustrated example, the position POS is at the endof the web 120 for ease of understanding. Note that, in the liquiddischarge apparatus, the sensor unit SEN may be disposed below the web120 (on the back side (opposite side) of the web 120 when the imageformation face serving as a front side), and the position POS may bedetected with reference to the end of the web 120.

To suppress misalignment in color superimposition of other color inks onthe black ink, the calculator 53F substrates, from the currentorthogonal position of the web 120 detected by the sensor unit SEN, theorthogonal position of the web 120 in the immediately previous detectionperiod, thereby calculating the displacement of the web 120.Specifically, the calculator 53F calculates a difference Pk between theorthogonal position of the web 120 detected by the sensor unit SENK andthe orthogonal position of the web 120 below the liquid discharge headunit 210K. Similarly, the calculator 53F calculates a difference Pcbetween the orthogonal position of the web 120 detected by the sensorunit SENC and the orthogonal position of the web 120 below the liquiddischarge head unit 210C. Similarly, the calculator 53F calculates adifference Pm between the orthogonal position of the web 120 detected bythe sensor unit SENM and the orthogonal position of the web 120 belowthe liquid discharge head unit 210M. Similarly, the calculator 53Fcalculates a difference Py between the orthogonal position of the web120 detected by the sensor unit SENY and the orthogonal position of theweb 120 below the liquid discharge head unit 210Y.

The differences between the droplet strike positions, at which the inkdroplets discharged from the liquid discharge head units 210 strike theweb 120, and the end of the web 120 are referred to as differences Lk3,Lc3, Lm3, and Ly3. Since the sensor units SEN detect the orthogonalposition of the web 120, each of the differences Pk, Pc, Pm, and Py is0. Such relations are expressed by the following formulas.Lc3=Lk3−Pc=Lk3Lm3=Lk3Ly3=Lk3−Py=Lk3  Formula 5

According to Formula 5, the relation “Lk3=Lm3=Lc3=Ly3” is obtained.Thus, the controller 520 (the head controller 54F) controls actuator(AC1, AC2, AC3, or AC4 in FIG. 18) to move the liquid discharge headunit 210 in response to the displacement of the web 120, and the imageforming apparatus 110 can improve the accuracy of droplet strikeposition in the orthogonal direction 20. As the accuracy of dropletstrike position improves, misalignment in color superimposition issuppressed, thereby improving the image quality.

In other words, when the position of the liquid discharge head unit 210is adjusted during image formation to enhance the accuracy of dropletstrike position, image quality can improve.

The sensor unit SEN is preferably disposed closer to the first rollerCR1 than the ink discharge position.

Referring to FIG. 17, descriptions are given below of one exampleposition of the sensor unit SEN, for example, of black. In this example,the sensor unit SENK for black is disposed between the first roller CR1Kand the second roller CR2K, more specifically, between the black inkdischarge position PK and the first roller CR1K (closer to the firstroller CR1K than the black ink discharge position PK) in the conveyancedirection 10. The distance of the sensor unit SENK from the black inkdischarge position PK toward the first roller CR1K is determined by thetime required for control operation. For example, the sensor unit SENKis at 20 mm (upstream by 20 mm in the conveyance direction 10) from theblack ink discharge position PK toward the first roller CR1K.

When the location of the sensor unit SEN is close to the ink dischargeposition, detection error E1 is suppressed, and the accuracy of dropletstrike position on the recording medium can improve. As the accuracy ofdroplet strike position improves, misalignment in color superimpositionis suppressed, thereby improving the image quality.

Such a configuration is free of layout constraint of setting thedistance between the adjacent two liquid discharge head units 210 to anintegral multiple of a length of circumference of the roller 230 (i.e.,a circumference distance d illustrated in FIG. 16A). Thus, position ofthe liquid discharge head unit 210 is determined more flexibly. That is,even when the distance between the adjacent two liquid discharge headunits 210 is not an integral multiple of the circumference length d ofthe roller 230, the accuracy of droplet strike position of each colorink is improved.

FIG. 18 is a plan view of the sensor units SEN according to anembodiment. The sensor units SEN are disposed such that detection rangesthereof overlap with the web 120 in the width direction (the orthogonaldirection 20). In FIG. 18, the sensor units SENK, SENC, SENM, and SENYare respectively disposed at positions PS1, PS2, PS3, and PS4, which arewithin the area of the web 120 in the orthogonal direction 20. The imageforming apparatus 110 controls the actuators AC1, AC2, AC3, and AC4 tomove the liquid discharge head units 210K, 210C, 210M, and 210Y in theorthogonal direction 20, respectively.

In FIG. 18, the sensor units SEN are disposed facing the liquiddischarge head units 210, respectively, via the web 120. Each sensorunit SEN includes a light-emitting element to emit light (e.g., laserlight) onto the web 120 and an image sensor to image a range of the web120 irradiated with the light emitted from the light-emitting element.

As the laser light emitted from the light-emitting element is diffusedon the surface of the web 120 and superimposed diffusion waves interferewith each other, a pattern such as a speckle pattern appears. The imagesensor of the sensor unit SEN captures and images such a specklepattern. Based on the change of position of the pattern captured by theimage sensor, the controller 520 (or the calculator 53F) can obtain theamount by which the liquid discharge head unit 210 is to be moved.

Additionally, in this structure, the liquid discharge head unit 210 andthe sensor unit SEN are preferably disposed such that the operation area(e.g., the image formation area) of the liquid discharge head unit 210overlaps, at least partly, with the detection range of the sensor unitSEN.

COMPARATIVE EXAMPLE 1

FIG. 19 is a plan view of the web 120 conveyed in a liquid dischargeapparatus 110X according to Comparative example 1. In the comparativeexample illustrated in FIG. 19, the orthogonal position of the web 120is detected before a given portion of the web 120 reaches the inkdischarge position of the liquid discharge head unit 210 (210K, 210C,210M, or 210Y). In Comparative example 1, each sensor unit SEN (SENK,SENC, SENM, and SENY) is disposed, for example, 200 mm upstream from aposition directly below the liquid discharge head unit 210 in theconveyance direction 10. In Comparative example 1, based on detection bythe sensor unit SEN, a controller 520X controls the actuator to move theliquid discharge head unit 210 to compensate for displacement(meandering) of the web 120 (e.g., a recording medium) in the inkdischarge position.

With reference to FIG. 20, descriptions are given below of processingperformed by the liquid discharge apparatus 110X according toComparative example 1. In Comparative example 1, the distance betweenthe adjacent two liquid discharge head units 210 is an integral multipleof the circumference distanced of the roller 230. In this case, thedifference (Pk, Pc, Pm, or Pm) between the orthogonal position of theweb 120 detected by the sensor unit SEN and that at the positiondirectly below the liquid discharge head unit 210 is “0”. Thus, inComparative example 1, the distances Lk1, Lc1, Lm1, and Ly1 of thedroplet strike positions of black, cyan, magenta, and yellow from theend of the web 120, in the width direction, are in the relation“Lk1=Lc1=Lm1=Ly1”.

With reference to FIG. 21, descriptions are given below of processingperformed by the liquid discharge apparatus 110X according toComparative example 2. The hardware configuration of Comparative example2 is similar to that of Comparative example 1. Comparative example 2 isdifferent from Comparative example 1 in that the distance between theliquid discharge head units 210K and 210C is 1.75 times longer than thecircumference distance d of the roller 230 and the distance between theliquid discharge head units 210M and 210Y is 1.75 times longer than thecircumference distance d. That is, the distance between the liquiddischarge head units 210 and 210 for black and cyan and the distancebetween the liquid discharge head units 210 and 210 for magenta andyellow is not integral multiple of the circumference length d of theroller 230.

In comparative example 2, the difference (Pk, Pc, Pm, and Py) betweenthe orthogonal position of the web 120 detected by the sensor unit SENand the orthogonal position of the web 120 below the correspondingliquid discharge head unit 210 for respective colors and the distancesLk1, Lc1, Lm1, and Ly1 of the droplet strike positions of black, cyan,magenta, and yellow from the end of the web 120 in the width directionare expressed by the following formulas.Lc2=Lk2−PcLm2=Lk2Ly2=Lk2−Py  Formula 6

Accordingly, the relation “Lk2=Lm2≢Lc2=Ly2” is obtained. In thiscomparative example, when the distance between the adjacent two liquiddischarge head units 210 is not an integral multiple of thecircumference distance d of the roller 230, the orthogonal positions ofthe web 120 directly below the liquid discharge head unit 210C and theliquid discharge head unit 210M is shifted by the differences Pc and Py,respectively. Accordingly, fluctuations in the orthogonal position ofthe web 120 are not compensated for in the ink discharge position,allowing misalignment in color superimposition.

FIG. 22 illustrates a location of the sensor unit SEN in the liquid inanother comparative example. In the arrangement in which the sensor unitSENK is away from the black ink discharge position PK as in FIG. 22, adetection error E2 is likely to be large.

FIG. 23 is a schematic view of the conveyed object detector 500according to the present embodiment, to detect the web 120. Asillustrated in FIG. 23, the first light source 51A, the second lightsource 51B, and an area sensor 11 are often contained in a case 13. Thecase 13 has an optical window LP made of a material having a hightransmittancy so that the optical systems, such as he area sensor 11 andthe first imaging lens 12A (or the second imaging lens 12B), containedtherein receive light reflected on the web 120. Thus, the case 13 andthe optical window LP thereof provide dustproofing for the opticalsystems of the conveyed object detector 500 to reduce effects of stain(e.g., paper dust).

Although the adhering object BD (e.g., ink or paper dust) may adhere,for example, to the optical window LP, the effect of the adhering dustBD is suppressed through the processing illustrated in FIG. 12.

Functional Configuration

FIG. 24 is a schematic block diagram of a functional configuration ofthe conveyed object detector 500. In the configuration illustrated inFIG. 24, the conveyed object detector 500 includes one image obtainingunit 52 (52A, 52B, 52C or 52D) for each of the plurality of liquiddischarge head units 210. The conveyed object detector 500 furtherincludes the calculator 53F, the recognition unit 56F, and the removalunit 57F.

In the example structure illustrated in FIG. 24, there are four imageobtaining units 52 (equivalent to the image obtaining units 52A and 52Bin FIG. 6). The image obtaining unit 52 detects the position of the web120 (the recording medium) in either the conveyance direction 10 or theorthogonal direction 20. The image obtaining unit 52 is implemented bythe sensor unit SEN illustrated in FIG. 5. The image obtaining unit 52outputs, using an optical sensor, a detection result indicating thespeed of movement of the conveyed object in at least one of theconveyance direction 10 and the orthogonal direction 20. The detectionresult includes the amount of movement in the conveyance direction 10and the orthogonal direction 20.

For each liquid discharge head unit 210, one first roller CR1 isprovided. In the example structure illustrated in FIG. 24, the number ofthe first rollers CR1 is four and identical to the number of the liquiddischarge head units 210. The first roller CR1 is disposed upstream fromeach liquid discharge head unit 210 to convey the web 120 to the inkdischarge position at which the liquid discharge head unit 210discharges liquid. In the case of black, the first roller CR1Killustrated in FIG. 2 is the first roller CR1.

Further, for each liquid discharge head unit 210, the second roller CR2is provided. In the example structure illustrated in FIG. 2, the numberof the second rollers CR2 is four and identical to the number of theliquid discharge head units 210. The second roller CR2 is disposeddownstream from each liquid discharge head unit 210 to convey the web120 away from the ink discharge position. In the case of black, thesecond roller CR2K illustrated in FIG. 2 is the second roller CR2.

The recognition unit 56F recognizes an object adhering to the imageobtaining unit 52 or the optical component used by the image obtainingunit 52. The detection method of the recognition unit 56F is describedabove with reference to FIGS. 13A, 13B, and 13C. The recognition unit56F is implemented by, for example, an electronic circuit.

The removal unit 57F removes the adhering object from the image datagenerated by the image obtaining unit 52. The removal unit 57F isimplemented by, for example, an electronic circuit.

The image forming apparatus 110 further includes a head moving device(e.g., the actuators AC1, AC2, AC3, and AC4) to move the liquiddischarge head units 210 according to the detection results.

As described above, the image obtaining unit 52 (e.g., the sensor unitSEN) is disposed in the inter-roller range INT1 (NTY1, INTC1, INTM1, orINTY1) close to the ink discharge position (PK, PC, PM, or PY) toenhance the detection accuracy of the position of the recording mediumin the conveyance direction 10 or the orthogonal direction 20.

More preferably, the image obtaining unit 52 (e.g., the sensor unit SEN)is disposed in the upstream range INTK2, INTC2, INTM2, or INTY2)upstream from the ink discharge position and downstream from the firstroller CR1 in the conveyance direction 10 to enhance the detectionaccuracy.

As described above, the embodiments described above concern the conveyedobject detector 500 and the liquid discharge apparatus (e.g., the imageforming apparatus 110) including the conveyed object detector. Theconveyed object detector 500 includes the image obtaining unit 52, therecognition unit 56F, and the removal unit 57F. The conveyed objectdetector 500 is configured to recognize an adhering object adhering suchas stain on the optical system and remove the adhering object from theimage data used in determining the position of the conveyed object.Then, the conveyed object detector 500 can detect the position of theconveyed object in either the conveyed direction 10 or the orthogonaldirection 20 with a high accuracy.

According to one aspect of this disclosure, for each liquid dischargehead unit, the liquid discharge apparatus includes the sensor unit(e.g., the sensor unit SEN) to detect the position of the conveyedobject (in either the conveyance direction 10 or the orthogonaldirection 20) at a position relatively close to the liquid dischargehead unit. According to the detection result, the liquid dischargeapparatus moves the liquid discharge head unit. In particular, in theliquid discharge apparatus, image quality is improved when the liquiddischarge head unit is moved to eliminate the misalignment in dropletstrike positions during image formation.

Accordingly, compared with Comparative examples 1 and 2 illustrated inFIGS. 20, 21, and 22, the liquid discharge apparatus according oneaspect of this disclosure can suppress the misalignment in the dropletstrike positions in the orthogonal direction 20.

Further, the image forming apparatus 110 illustrated in FIG. 2 is freeof layout constraint required in Comparative example 1, that is, arequisite of setting the distance between the adjacent two liquiddischarge head units to an integral multiple of the length ofcircumference of the driving roller. Thus, layout of the liquiddischarge head units is more flexible in the structure illustrated inFIG. 2.

As the accuracy in droplet strike positions improves, misalignment incolor superimposition is suppressed, improving image quality.

Variation

FIG. 25 is a schematic block diagram of the conveyed object detector 500including an imaging unit 161 according to Variation 1. The imaging unit161 is configured as if two imaging units 16 illustrated in FIG. 6 arecombined therein. The imaging controller 14, the image memory 15, andthe calculator 53F are similar to those illustrated in FIGS. 4 and 6.

The first light source 51A and the second light source 51B emit laserlight or the like to the web 120, which is an example of the conveyedobject to be detected. The first light source 51A irradiates a positionA with light, and the second light source 51B irradiates a position Bwith light.

The light sources 51 are not limited to laser light sources but can belight emitting diodes (LEDs) or the like.

Each of the first light source 51A and the second light source 51Bincludes a light-emitting element to emit laser light and a collimatorlens to approximately collimate the laser light emitted from thelight-emitting element. The first light source 51A and the second lightsource 51B are disposed to emit light in an oblique direction relativeto the surface of the web 120.

The imaging unit 161 includes the area sensor 11, the first imaging lens121 disposed opposing the position A, and the second imaging lens 12Bdisposed opposing the position B.

The area sensor 11 includes an image sensor 112 on a silicon substrate111. The image sensor 112 includes an area 11A and an area 11B, in eachof which a two-dimensional image is captured. For example, the areasensor 11 is a CCD sensor, a complementary metal oxide semiconductor(CMOS) sensor, a photodiode array, or the like. The area sensor 11 ishoused in a case 13. The first imaging lens 12A and the second imaginglens 12B are hold by first lens barrel 13A and a second lens barrel 13B,respectively.

In the illustrated structure, the optical axis of the first imaging lens12A matches a center of the area 11A. Similarly, the optical axis of thesecond imaging lens 12B matches a center of the area 11B. The firstimaging lens 12A and the second imaging lens 12B focus light on the area11A and the area 11B, respectively, to generate two-dimensional images.

FIG. 26 is a schematic view of an imaging unit 162 according toVariation 2. Differently from the structure illustrated in FIG. 25, inthe structure illustrated in FIG. 26, the first imaging lens 12A and thesecond imaging lens 12B are integrated into a lens 12C. The area sensor11 and the like are similar in structure to those illustrated in FIG. 4.

Additionally, in this structure, use of aperture 121 or the like ispreferable to prevent interference between the images generated by thefirst imaging lens 12A and the second imaging lens 12B. The aperture 121or the like can limit a range in which each of the first imaging lens12A and the second imaging lens 12B generates an image. Accordingly, theinterference between the images are suppressed. Then, the imaging unit162 can generate an image of the position A and an image of the positionB illustrated in FIG. 26.

FIGS. 27A and 27B are schematic views of an imaging unit 163 accordingto Variation 3. Differently from the structure illustrated in FIG. 25,the imaging unit 163 illustrated in FIG. 27A includes an area sensor 11′instead of the area sensor 11. The first imaging lens 12A, the secondimaging lens 12B, and the like are similar in structure to thoseillustrated in FIG. 5.

The area sensor 11′ has a structure illustrated in FIG. 27B, forexample. Specifically, as illustrated in FIG. 27B, a wafer 11 a includesa plurality of image sensors b. The plurality of image sensors billustrated in FIG. 27B is cut out of the wafer 11 a. The plurality ofimage sensors b serves as a first image sensor 112A and a second imagesensor 112B and disposed on the silicon substrate 111. The first imaginglens 12A and the second imaging lens 12B are disposed in accordance withthe distance between the first image sensor 112A and the second imagesensor 112B.

Image sensors are generally manufactured for imaging. Therefore, imagesensors have an aspect ratio (ratio between X-direction size andY-direction size), such as square, 4:3, and 16:9, that fits an imageformat. In the present embodiment, an image covering at least twodifferent points spaced apart is captured. Specifically, an image iscaptured at each of points spaced apart in the X direction, onedirection in two dimensions. The X direction corresponds to theconveyance direction 10 illustrated in FIG. 4. By contrast, the imagesensor has an aspect ratio fit for the image format. Accordingly, whenan image is captured at the two points spaced apart in the X direction,it is possible that an image sensor relating to the Y direction is notused. To enhance pixel density, an image sensor having a higher pixeldensity is used in either the X direction or the Y direction. In such acase, the cost increases.

In view of the foregoing, in the structure illustrated in FIG. 27A, onthe silicon substrate 111, the first image sensor 112A and the secondimage sensor 112B spaced apart are disposed. This structure can reducethe number of unused image sensors of the image sensors relating to theY direction. In other words, waste of image sensors is inhibited.Additionally, since the first image sensor 112A and the second imagesensor 112B are produced through a semiconductor process with highaccuracy, the distance between the first image sensor 112A and thesecond image sensor 112B is set with high accuracy.

FIG. 28 is a schematic view of a plurality of imaging lenses used in theimaging unit 16 according to another variation. The lens arrayillustrated can be used to implement the image obtaining unit 52.

In the lens array illustrated in FIG. 28, two or more lenses areintegrated. Specifically, the lens array illustrated in FIG. 28includes, for example, nine imaging lenses A1, A2, A3, B1, B2, B3, C1,C2, and C3 arranged in three rows and three columns. When such an lensarray is used, an image including nine points is captured. In this case,an area sensor having nine imaging ranges is used.

In this structure, for example, arithmetic of the two imaging ranges canbe performed concurrently, that is, in parallel. When the results ofarithmetic of each range are averaged, or error is removed from theresults, the accuracy and stability of arithmetic can be higher,compared with a case in which one arithmetic result is used. There arecases where the arithmetic is performed based on application software,the speed of which fluctuates. Even in such case, accurate result ofarithmetic can be obtained since a range for performing correlationoperation is expanded.

Referring back to FIG. 25, the imaging controller 14 controls theimaging unit 161 (or 162 or 163). Specifically, for example, the imagingcontroller 14 outputs signals to the imaging unit 161 to control thetiming of shooting (shutter timing) of the area sensor 11. The imagingcontroller 14 causes the imaging unit 161 to generate thetwo-dimensional images and acquires the two-dimensional imagestherefrom. Then, the imaging controller 14 transmits the two-dimensionalimages to the image memory 15.

The image memory 15 is a so-called memory. The conveyed object detector500 preferably has a capability to divide the two-dimensional imagestransmitted from the imaging controller 14 and storing the dividedimages in different memory ranges.

For example, the calculator 53F is a microcomputer. The calculator 53Fperforms operations using the image data stored in the image memory 15and the like, to implement a variety of processing.

The imaging controller 14 and the calculator 53F are, for example,central processing units (CPUs) or electronic circuits. Note that theimaging controller 14, the image memory 15, and the calculator 53F arenot necessarily discrete devices. For example, the imaging controller 14and the calculator 53F can be implemented by a single CPU.

FIG. 29 is a schematic view of the image forming apparatus 110 (e.g., aliquid discharge apparatus) according to a variation. The configurationillustrated in FIG. 29 differs from the configuration illustrated inFIG. 2 regarding the locations of the first support and the secondsupport. The structure illustrated in FIG. 29 includes supports RL1,RL2, RL3, RL4, and RL5, serving as the first and second supports, tosupport the web 120. In other words, the second support (e.g., theconveyance roller CR2K in FIG. 2) disposed downstream from the upstreamone of adjacent two head units also serves as the first support (e.g.,the conveyance roller CR1C in FIG. 2) disposed upstream from thedownstream one of the adjacent two head units. Note that, the supportaccording to the variation, which doubles as the first and secondsupports, can be either a roller or a curved plate.

One or more of aspects of this disclosure can adapt to a liquiddischarge system including at least one liquid discharge apparatus. Forexample, the liquid discharge head unit 210K and the liquid dischargehead unit 210C are housed in one case as one device, and the liquiddischarge head unit 210M and the liquid discharge head unit 210Y arehoused in another case as another device. Then, the liquid dischargesystem includes the two devices.

Further, one or more of aspects of this disclosure can adapt a liquiddischarge system to discharge liquid other than ink. For example, theliquid is a recording liquid of another type or a fixing solution.

The liquid discharge apparatus (or system) to which one or more ofaspects of this disclosure is applicable is not limited to image formingapparatus to form two-dimensional images but can be apparatuses tofabricate three-dimensional articles.

The recording medium is not limited to recording sheets but can be anymaterial to which liquid adheres, even temporarily. Examples of thematerial to which liquid adheres include paper, thread, fiber, cloth,leather, metal, plastic, glass, wood, ceramics, and a combinationthereof.

Further, one or more of aspects of this disclosure is applicable to amethod of discharging liquid from an image forming apparatus, aninformation processing apparatus, or a computer as a combinationthereof, and at least a portion of the method can be implemented by aprogram.

Further, one or more of aspects of this disclosure can adapt to anyconfiguration (in the form of apparatus, method, system, computerprogram, and computer program product) in which an apparatus performs anoperation on a conveyed object or processing of the conveyed object,using a head to move in the direction orthogonal to the direction ofconveyance of the conveyed object. For example, one or more of aspectsof this disclosure can adapt to a configuration in which a laser headmoves in the direction orthogonal to the direction of conveyance of asubstrate being a conveyed object. The laser head performs laserpatterning on the substrate extends, and the laser head is movedaccording to detection of position of the substrate.

The number of the head units is not necessarily to two or more. In otherwords, one or more of aspects of this disclosure can adapt to anapparatus configured to keep applying an object discharged from a headunit to a reference position. In the case of a laser device, the deviceis configured to keep writing on a reference position.

Any one of the above-described operations may be performed in variousother ways, for example, in an order different from the one describedabove. Any of the aforementioned methods may be embodied in the form ofa program. The program may be stored on a computer readable media and isadapted to perform any one of the aforementioned methods when run on acomputer device (a device including a processor). Thus, the storagemedium or computer readable medium, is adapted to store information andis adapted to interact with a data processing facility or computerdevice to perform the method of any of the above mentioned embodiments.

Each of the functions of the described embodiments may be implemented byone or more processing circuits or circuitry. Processing circuitryincludes a programmed processor, as a processor includes circuitry. Aprocessing circuit also includes devices such as an application specificintegrated circuit (ASIC), DSP (digital signal processor), FPGA (fieldprogrammable gate array) and conventional circuit components arranged toperform the recited functions.

The above-described embodiments are illustrative and do not limit thepresent invention. Thus, numerous additional modifications andvariations are possible in light of the above teachings. For example,elements and/or features of different illustrative embodiments may becombined with each other and/or substituted for each other within thescope of the present invention.

What is claimed is:
 1. A conveyed object detector comprising: a firstimage obtaining unit disposed at a first position to image a conveyedobject to obtain first image data corresponding to a plurality of imagesof the conveyed object before image formation and while the conveyedobject is moving in a conveyance direction; a second image obtainingunit disposed at a second position downstream from the first position ina conveyance direction of the conveyed object, the second imageobtaining unit configured to image the conveyed object to obtain secondimage data corresponding to the plurality of images of the conveyedobject before image formation and while the conveyed object is moving ina conveyance direction, each of the first image obtaining unit and thesecond image obtaining unit including: a light source to irradiate theconveyed object with light; an area sensor to receive reflected lightreflected from the conveyed object; and an optical element disposedbetween the area sensor and the conveyed object; a controller configuredto, before image formation, recognize an object adhering to the firstimage obtaining unit based on the obtained first image data to generatefirst stain data; recognize an object adhering to the second imageobtaining unit based on the obtained second image data to generatesecond stain data; remove the first stain data from the first imagedata, to generate first corrected image data; remove the second staindata from the second image data to generate second corrected image data;and generate, as a calculation result, at least one of a position, amovement amount, and a moving speed of the conveyed object based on thefirst corrected image data and the second corrected image data.
 2. Theconveyed object detector according to claim 1, wherein the first imageobtaining unit and the second image obtaining unit are configured toimage a pattern on the conveyed object, and wherein the controller isconfigured to generate the calculation result with reference to thepattern.
 3. The conveyed object detector according to claim 2, whereinthe pattern represents interference of the reflected light on a ruggedshape of the conveyed object, and the controller is configured togenerate the calculation result based on an image of the pattern.
 4. Theconveyed object detector according to claim 2, wherein the first imageobtaining unit is configured to image the pattern at a first time pointto obtain the first image data, wherein the second image obtaining unitis configured to image the pattern at a second time point different fromthe first time point, to obtain the second image data, and wherein thecontroller is configured to calculate a position of the conveyed objectin an orthogonal direction orthogonal to the conveyance direction, basedon the first corrected image data and the second corrected image data.5. The conveyed object detector according to claim 1, wherein thecontroller is configured to: superimpose a plurality of image dataoutput by the first image obtaining unit to generate the first staindata; and superimpose a plurality of image data output by the secondimage obtaining unit to generate the second stain data.
 6. A conveyancedevice comprising: a conveyor to convey the conveyed object; and theconveyed object detector according to claim
 1. 7. An apparatuscomprising: a head unit to move in an orthogonal direction orthogonal tothe conveyance direction and perform an operation on the conveyedobject; the conveyance device according to claim 6; and a headcontroller to control the head unit, based on the calculation resultgenerated by the conveyed object detector.
 8. The apparatus according toclaim 7, further comprising: a first support disposed upstream from thehead unit in the conveyance direction; and a second support disposeddownstream from the head unit in the conveyance direction, wherein oneof the first image obtaining unit and the second image obtaining unit isdisposed between the first support and the second support in theconveyance direction.
 9. The apparatus according to claim 8, wherein theimage obtaining unit is disposed between the head unit and the firstsupport in the conveyance direction.
 10. The apparatus according toclaim 7, further comprising a head moving device to move the head unitin the orthogonal direction.
 11. The apparatus according to claim 7,wherein the head controller is configured to determine a position of thehead unit based on the calculation result generated by the conveyedobject detector.
 12. The apparatus according to claim 7, wherein theconveyed object is a continuous sheet.
 13. The apparatus according toclaim 7, wherein the head unit includes a liquid discharge head toperform, as the operation, image formation on the conveyed object.
 14. Aconveyed object detector comprising: image obtaining means for imaging aconveyed object at a first position and at a second position downstreamfrom the first position before image formation and to obtain first imagedata and second image data, respectively, the second position differentfrom the first position in a conveyance direction of the conveyedobject; recognition means for recognizing, before image formation, anadhering object based on imaging at the first position to generate firststain data; and an adhering object based on imaging at the secondposition to generate second stain data; removal means for removing thefirst stain data from the first image data to generate first correctedimage data and removing the second stain data from the second image datato generate second corrected image data; and calculating means forgenerating, as a calculation result, at least one of a position, amovement amount, and a moving speed of the conveyed object based on thefirst corrected image data and the second corrected image data.
 15. Aconveyed object detecting method comprising: imaging, with a first areasensor and a second area sensor, a conveyed object at a first positionand a second position downstream from the first position to obtain firstimage data and second image data before image formation, respectively,the second position different from the first position in a conveyancedirection of the conveyed object; recognizing, before image formation,an adhering object adhering to the first area sensor based on imaging atthe first position, to generate first stain data; recognizing, beforeimage formation, an adhering object adhering to the second area sensorbased on imaging at the second position, to generate second stain data;removing the first stain data from the first image data, to generatefirst corrected image data; removing the second stain data from thesecond image data, to generate second corrected image data; andgenerating, as a calculation result, at least one of a position, amovement amount, and a moving speed of the conveyed object based on thefirst corrected image data and the second corrected image data.
 16. Acomputer-readable non-transitory recording medium storing a program forcausing a computer to execute the method according to claim 15.